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Toshiba RPTV 50H72 - blue screen only

Discussion in 'Electronic Repair' started by bharat, May 1, 2004.

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  1. bharat

    bharat Guest

    This TV only shows blue screen. When I go into setup, I can see that
    red and green CRTs are working (I see green and red colors) but the
    screen background stays blue. When I connect a DVD player, the screen
    briefly shows real picture but then turns completely blue. Ditto when
    I turn the TV off with DVD running (picture shows for an instant
    before TV turns OFF). I think video apms that drive yokes are
    suspect..but wanted to confirm with someone before I order the ICs and
    replace them. I checked all power supplies and they are OK (specially
    to the video amp ICs). All components I checked seem fine (atleast
    the ones I checked showed appropriate behavior). Any suggestions are

  2. Jerry G.

    Jerry G. Guest

    There may be a loss of sync to the scan circuits, or there may be a response
    problem in the video path, thus not allowing proper sync. You would have to
    get the service manual, and trace through with a scope to see where this
    type of fault is. Also, checking for the proper supply voltages in the
    various stages would be a proper thing to do.

    If you are not trained and equipped in TV service, I would suggest to have
    the set properly looked after.



    Jerry Greenberg GLG Technologies GLG

    This TV only shows blue screen. When I go into setup, I can see that
    red and green CRTs are working (I see green and red colors) but the
    screen background stays blue. When I connect a DVD player, the screen
    briefly shows real picture but then turns completely blue. Ditto when
    I turn the TV off with DVD running (picture shows for an instant
    before TV turns OFF). I think video apms that drive yokes are
    suspect..but wanted to confirm with someone before I order the ICs and
    replace them. I checked all power supplies and they are OK (specially
    to the video amp ICs). All components I checked seem fine (atleast
    the ones I checked showed appropriate behavior). Any suggestions are

  3. David

    David Guest

    Ditto on the find someone who knows what they are doing.

    This statement (typo fixed) clearly indicates a total lack of understanding
    of what is going on inside the set:
    " I think video amps that drive yokes are suspect."

  4. bharat

    bharat Guest

    This newsgroup is for help. If you cannot provide any help, please
    stay off the line. If I knew what was wrong, I would not have posted
    the article in the first place. There was a post previously in this
    newsgroup where the person was seeing all green screen...the hints
    were for checking the video amps. So I assumed that would be a first
    place to start.

    Your typo-corrected sentence is same as mine. May be you should get
    some education before getting on the net, you [email protected]#$%^! Send me your
    email address and we can take this discussion about your intelligence
    and mine off the newsgroup.

  5. David

    David Guest

    So what is an apms?
    It still is clear in your posting that you have no clue how a tv set or rptv

    We just went through court because someone idiot bought a part from us (we
    looked up the part number at his request) and the idiot wound up catching
    the tv and house on fire!!!!! So he tried to sue us!!!

    So don't go telling me that you think you know what you are doing when it is
    clear in your post that you do not. Assuming what you said was video amps,
    video amps do not drive yokes, period.
  6. Art

    Art Guest

    Get the flippin set to a Qualified Service Company or consider replacing it
    with a new one. It is perfectly obvious that you do not have the
    qualifications to be attempting to service this product competently. Do
    yourself a BIG Favor and have it done by the folk who do know how to do it
    efficiently and safely.
  7. Agreed. Pay a little now, or a lot later. That's an excellent TV - it's worth a
    couple bucks to get it repaired.

    Alan Harriman
  8. Eugen T

    Eugen T Guest

    Wow, I have never seen so many arrogant people in one newsgroup at the same
    If you can't help, then just don't say anything.
  9. David

    David Guest

    We are helping him. If someone clearly has no clue what is going on, they
    are probably going to do one of two things when they attempt to repair
    something as complex as a tv set: 1. damage it beyond reasonable and
    practical repair when they finally take it into someone qualified. or 2.
    Get into something they shouldn't have and cause some potentially lethal or
    serious injury to themselves.
  10. bharat

    bharat Guest

    Let me make a few things clear to answer your [email protected]#$%^&*() arrogance.

    Video amps are video amplifiers located in Q751 and Q752 on the signal
    board. They drive yokes directly. In case any of you arrogant morons
    had time and knowledge to understand what a schmatic looks like, you
    would clearly see where video amplifiers are located. In adition,
    amps is shorthand for amplifiers - any person knowledgable in
    Electrical Engineering knows that. Next time, try to understand the
    posting before replying. Your assumption that if you do not
    understand something then it must be wrong is stupid!

    Secondly, a while back in this newsgroup, there was a posting where
    someone had green screen problem similar to mine. The solution posted
    on the net was that the power supply to video amplifiers was suspect.
    Hence my intuition regarding video amps (oops, I mean video amplifiers
    for you intellectually-challenged guys).

    Many of us know and understand the danger in repairing a TV set - not
    just you arrogant [email protected]$$%&*.

    By the way, I have a PhD in electrical engineering and probably can
    run circles around you when it comes to knowledge of electrical
    engineering. However, I do not know specifically how to fix a TV and
    hence the posting. If I had the time, I can understand the circuit
    and then figure out what is wrong. I was hoping that this newsgroup,
    with its collective knowledge, will help me fix this. Your arrogant
    replies regarding "what is amps" itself shows that you do not have a
    clue as to what an "amplifier" is. Take a few educational courses (or
    read a book) before you start yelling at people.

    Again, this newsgroup is for help. If you can help, please by all
    means do so. If you do not understand what an "amps" is, do everyone
    a favor and stop wasting bandwidth.

    By the way, I am going to check the sync signals (for you stupids, it
    is synchronization signals) to see if the problem lies there as
    pointed out by more considerate members of this newsgroup. I thank

  11. David

    David Guest

    Video amps are video amplifiers located in Q751 and Q752 on the signal
    Video amplifiers do not drive yokes. Deflection circuitry drives deflection yokes. I have a PhD in electrical enginnering also, but not the attitude you have.

  12. Ken Weitzel

    Ken Weitzel Guest


    Darn, you guys are embarassing me. I only got to
    bachelor, and that only by the skin of my teeth.
    (Hey, someone had to finish at the bottom of the class,
    right? :)

    Now old, long retired, and a stroke victim. Spent a
    year couldn't walk, and a few years wondering who I
    was and why.

    I continue to get better, though, and can help a
    little here. I agree that it's a problem with
    the synchronization of his yokes. I suspect that
    his blue yoke has gone out of sync, and he's going
    to have to replace it.

    A quick test to verify this would be to temporarily
    switch the red and blue yoke (or the green and blue
    yoke) just to see if it improves.

    If it does, just call Toshiba or one of it's dealers
    and order a new blue yoke.

  13. David is completely correct, video amps don't drive yokes. I suppose they
    didn't teach you that in electrical engineering.

    Actually, Q751 and Q752 are convergence amplifiers, not video amplifiers,
    and are likely not your problem. If one of these failed you would see
    convergence problems, the set would shut down, or it would blow fuse(s) and
    shut down. If you are getting a blue screen it is likely that you have lost
    signal and the set is muting the video. Your problem could be anything
    from not knowing how to operate the set to a problem anywhere in the signal

    If you are looking for video amplifiers you are looking in the wrong area.
    You might want to check your assumptions and your reading of the schematic
    before losing it on a forum where you are asking for help. Your post
    indicated exactly what David noted, that you may be in over your head.

    Now, if you want some help, why not tell us what equipment you have, and
    what measurements you have taken and the signal conditions under which they
    were taken. A few of us arrogant morons, as you put it, have quite a lot of
    experience that we might be willing to share. Understand, however, that if
    you don't have the right equipment, knowledge, and troubleshooting skills,
    this may not be a realistic repair for you to attempt.

    Your attitude and your PhD will not necessarily help in fixing your set. A
    scope, some humility, and some TV service skills would go a lot farther.

    Pedantic asshole, maybe...arrogant moron, not usually
  14. Art

    Art Guest

    Absolute WASTE OF MY TIME!!! This flippin bloke is helpless, ignorant,
    stupid and don't even realize it. Blantely obvious he does not want
    assistance since he bloody knows everything about this device. Cheere,
    Mate, have a good live as and Electrical Engineer. I hope I never encounter
    any device you had any interest in designing or implimenting.
  15. Art

    Art Guest

    By The Way, the typos are intentional!! Maybe he just understands Phonics??
  16. David

    David Guest

    You are still totally clueless. Talk about a worthless phd if you really
    have one, which I doubt given the new post where you try and prove that you
    know what you are talking about.

    Not even close again. Q751 and Q752 are not video amps. (at least you
    spelled it correctly this time). They are AUDIO amplifier output ic's being
    used as convergence output amplifiers. I totally understood the posting and
    the fact that you did not understand electronics enough to try and attempt a

    It is even more clear that you have no business whatever your so called
    worthless paper degree is in to be inside the tv attempting a repair on it.
    Especially since you cannot read or spell, (apms vs amps, not the same thing
    dumbass) doubtful you have any college degree. I pity the reputation of any
    college that actually gave you a degree. At least you did not try and call
    it 'snyc' this time around.
  17. David

    David Guest

    If you only knew how sub-standard some college education really is these
    days, you would laugh.

    Some words of wisdom from my Father who hired engineers:

    Those that can do, those that can't teach.
    Never ever hire an engineer that was not a technician first, they cannot
    troubleshoot thier way out of a paperbag.
  18. bharat

    bharat Guest

    I haven't had this many arguments over a posting for a long time!!:)

    I own another 52H72 and have troubleshot the power board without any
    problem (it did take me a whole weekend to do it). That set kept
    turning on and off. I was hoping to avoid a repeat of my "lost"
    weekend. I wanted someone to point out the area I should be checking.
    I am not that familiar with the signal board and I believe people on
    the net have more experience than I will ever have repairing a TV.
    Hence the post. I did not want to post a lengthy note on what tests I
    did (I checked all power supply lines, H-sync, and yoke drivers. I
    have multimeters and a simple oscilloscope). I went through the
    schematic. Went through this newsgroup. A previous post mentioned
    video amps. There were amplifiers driving the yokes. I assumed that
    is what the previous message was talking about when it said video

    If I was wrong, please point it out and point me in the correct
    direction. Pointing out my inexperience in repairing a TV is
    acceptable, but not providing help and flaming me is not OK. There
    are hundreds of postings each day here. If you can't provide help,
    don't say anything. Everyone who reads this newsgroup knows (a) a lot
    of novices are attempting TV repair who should not, (b) TV repair is
    dangerous business, (c) most of these novices will harm themselves
    (darwinian principle at work) and learn along the way not to do it
    again (as David's post pointed out about the guy who burned his house

    Please do not assume that someone is not capable of understanding
    things regarding TV and repairing it. With a little help and some
    precautions (and common sense about electrical engineering), competent
    people can repair TVs. Newsgroups like this one certainly helps.

    I did not mean to offend collectively everyone (I was thinking no one
    will read this posting because it was old. And only David and I will
    scream at each other for a day and then forget about it). Obviously
    that is not the case.

    I am going to check yokes and sync signals. Hopefully, that will tell
    me more about where to go. Thanks for all the help.

  19. Ken Weitzel

    Ken Weitzel Guest


    Seeing as this message is a tiny bit apologetic, and a
    lot less arrogant, I'll take a chance and try again...
    hopefully a little has been learned (on both sides) and
    a fresh start is possible.

    I'll apologize for my message agreeing (sarcastically)
    with you, and hope we can do better.

    So, having said that, I'm an old stroke damaged
    retired guy who hasn't been in the picture for
    several years... just keeping in touch, so don't
    take my word either as gospel, or current :)

    What got everyone's dander up started with the yoke.
    The yoke has absolutely nothing, repeat nothing to
    do with your current problem. The yoke is that
    round coils of wire on the neck of the picture tube,
    pushed snugly up against the "flare" of the tube.
    It's sole purpose in life is deflection. It's
    driven by the horizontal and vertical ouputs.
    If the horizontal portion fails, you'll be left
    with (theoretically only) a bright white vertical
    line. If the vertical fails, you'll be left with
    (in reality) a straight white horizontal line across
    the center of the crt.

    So, let's leave the yoke out of it.

    Sync is responsible for synchronizing that
    vertical and horizontal deflection... failure
    will give you a "rolling" picture (vertical fail)
    or one that won't "stand straight up.

    So let's leave sync out of it.

    What have we left that IS perhaps responsible?

    Well, there is a possibility that the blue grid
    in the crt is shorted. This almost certainly makes
    the set not worth repair.

    There are drivers (transistors), one for each colour.
    These are most likely located on the pcb which is
    plugged onto the picture tube socket. The possiblity
    is that one is shorted. Check them easily enough
    by simply comparing them one against another with
    the other "set"

    Further than that I cannot go, not knowing your
    set or even much of the state of the art.

    But it's a start in the right direction, and perhaps
    can lead to more.

    I'll take a chance and give you one tiny little
    lecture and life lesson. I raised many kids,
    (all girls) and now am an old man all alone raising
    (trying) a just turned teenage grand daughter.
    I told each of them, and now I tell you, that how
    you treat other people is going to make a bigger
    difference in you life than any other thing you
    can do. More important than education, than skills,
    than wealth, than appearance, anything.

    Let's see where we go from here.

    Good luck, and take care.

  20. David

    David Guest

    Answer these questions and you might be able to narrow it down.
    Do you have a schematic?
    When the picture appears, does the color look good for the second? If so
    the tv is probably going into blue screen mute.
    Look to the system control (aka microcontroller/ micro) ic that basically
    runs everything first.
    You will may find OSD outputs RGB going to the jungle ic (term for the big
    signal process ic that does most everything). Look at the RBG outputs to
    see if the blue is on (more or less) all the time. If it is the micro is
    definitely putting the tv into blue screen mute. Then look for the signal
    sync going into the micro to see if it is present.

    The micro has several must signals in order to display a picture. H-sync
    (horizontal feedback sync from deflection) set will usually turn off if
    missing right away, V-Sync (vertical feedback sync from deflection) tv will
    typically shut down after 2 to 3 seconds, 60Hz clock signal from the ac
    power line (different sets behave strangely, could cause blue screen mute),
    a serial clock and data handshake from several other ics on the databus
    (since manufactures do not provide enough information to actually
    troubleshoot this, swap a part until it works, some tv sets have a computer
    interface and error code service mode to help), of course the micro needs
    the signal sync in order to know there is an image to display, we cannot
    forget about the AKB (auto-kine-bias) circuits on the picture tubes which
    can blank the video completely.

    Simple troubleshooting:
    1. Since the menu works, and if the audio goes up and down, or different
    video inputs can be selected via the remote control. This indicates that at
    least the data buss is functional and the ics are communications. It does
    not mean there not an ic that is not sending the all ok signal to the micro
    2. Since the video comes on for a second when immediately switching inputs,
    the set is most likely in blue screen mute.
    3. If the blue screen does not have the 10-12 visible diagonal retrace
    lines, this pretty much rules out the video output stages.
    4. Try the s-video or component inputs to see if they work as well. If the
    s-video works, it means there is a problem before or including the comb
    filter. If only the component video works even more of the signal circuit
    has been eliminated.
    5. Do not forget that this device has virtually all of its functional
    parameters (adjustments) set by an eeprom and service menu. Corrupted data
    in the wrong location can cause the same symptoms as actual parts failures.

    As an added note, I strongly recommend you use an isolation transformer for
    the tv set whenever working on it with the back removed. It will provide a
    level of safety to yourself and your test equipment that no measure of being
    careful can achieve. Even though that set uses a SMPS to provide isolation,
    there are still exposed components and traces tied directly to the AC power
    line source.

    After doing some research, I found out you really are at least a Professor
    at a college or university so you might have a PhD afterall, sorry for
    doubting your word. Don't take anything personal as it is hard to judge the
    character of someone from inaccurate information posted on the web. I have
    to go by experience and it has not been a good one with some people, as
    indicated with the fire and lawsuit.

    I have taught unemployed engineers in a course where they were retraining to
    become technicians. They were by far the worst students at "getting it"
    when it came to real world troubleshooting and circuit behavior.

    It should take about 15 minutes maximum to narrow down a close location of
    the problem.
    I always check the required stuff before going in very deep. Proper and
    clean Vcc and Vdd votlages. All the correct signals to the system control,
    60Hz ac pulse, H-sync, V-sync, Signal sync, clean Vcc, etc. Then move to
    the jungle ic. If the Signal sync is found missing or small, simply start
    tracing it back to its source (near the jungle ic I am sure).
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